Base station which relays cellular verification signals via a telephone wire network to verify a cellular radio telephone

ABSTRACT

A secure radio personal communication system and method includes a base station which relays cellular verification signals between a wide area cellular network and a cellular terminal via the wire telephone network. Thus, cellular telephone calls which are routed to a cellular terminal via a base station, when the cellular terminal is within a local region covered by the base station, may be exchanged between the cellular network and cellular terminal over the wire telephone network. Calls from the wide area cellular network which are routed through the base station can thus employ the same security systems and methods which are employed by the wide area cellular network. Signals between the base station and the cellular terminal are preferably exchanged when the cellular terminal is parked in the base station. Verification and encryption signals may be exchanged. The same signals may be used for enhanced security when the base station is relaying wire network calls to the cellular terminal when the cellular terminal is in the local region. Alternatively, separate verification and encryption protocols may be used.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of application Ser. No.08/148,828 filed on Nov. 4, 1993, now U.S. Pat. No. 5,428,668, andassigned to the assignee of the present invention, the disclosure ofwhich is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to communications systems and more particularlyto radio personal communications systems for use within wide areacellular networks.

BACKGROUND OF THE INVENTION

Radio communications systems are increasingly being used for wirelessmobile communications. An example of a radio communications system is acellular phone network. Cellular radio communications systems are widearea communications networks which utilize a frequency (channel) reusepattern. The design and operation of an analog cellular phone system isdescribed in an article entitled Advanced Mobile Phone Service byBlecher, IEEE Transactions on Vehicular Technology, Vol. VT29, No. 2,May, 1980, pp. 238-244. The analog mobile cellular system is alsoreferred to as the "AMPS" system.

Recently, digital cellular phone systems have also been proposed andimplemented using a Time-Division Multiple Access (TDMA) architecture.Standards have also been set by the Electronics Industries Association(EIA) and the Telecommunications Industries Association (TIA) for anAmerican Digital Cellular (ADC) architecture which is a dual mode analogand digital system following EIA/TIA document IS-54B. Telephones whichimplement the IS-54B dual mode architecture are presently being marketedby the assignee of the present invention. Different standards have beenpromulgated for digital cellular phone systems in Europe. The Europeandigital cellular system, also referred to as GSM, also uses a TDMAarchitecture.

Proposals have recently been made to expand the cellular phone networkinto a radio personal communications system. The radio personalcommunications system provides mobile radio voice, digital, video and/ormultimedia communications using radio personal communications terminals.Thus, any form of information may be sent and received. Radio personalcommunications terminals include a radio telephone, such as a cellulartelephone, and may include other components for voice, digital, videoand/or multimedia communications.

A radio personal communications system includes at least one telephonebase station, also referred to herein as a "base station". A basestation is a low power transceiver which communicates with a radiopersonal communications terminal such as a cellular telephone over alimited distance, such as tens of meters, and is also electricallyconnected to the conventional public wire telephone network. The basestation allows the owner of a radio personal communications terminal todirectly access the wire telephone network without passing through thecellular phone network, whose access rates are typically more costly.When located outside the range of the base station, the personalcommunications terminal automatically communicates with the cellularphone network at the prevailing access rates.

A major problem in implementing a radio personal communications systemis security for communications between the base station and the personalcommunications terminal. Modern cellular telephone networks includesecurity systems and methods to prevent eavesdropping and telephonefraud. Eavesdropping may be prevented by using encryption of radiotransmissions between a cellular phone and a cellular network. Fraud maybe prevented by preventing radio telephone transmissions between thecellular phone and the cellular network unless identificationinformation is successfully exchanged between the cellular phone and thecellular network. Existing cellular systems, such as the AMPS system,the ADC system, and the GSM system each include their own securitysystems and methods. Security should not be compromised bycommunications between the radio personal communications terminal andthe base station of a radio personal communications system.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved radio personal communications system including a base stationand a radio personal communications terminal, and methods for using thesame.

It is another object of the present invention to provide radio personalcommunications systems which do not compromise security of a wide areacellular system with which they interact.

In the present invention, a base station connects a wire telephonenetwork to a radio personal communications terminal, also referred toherein as a "cellular terminal" or simply a "terminal", within a localregion of a wide area cellular network. The base station includes a wiretelephone network connector, for connecting the base station to the wiretelephone network. The base station relays cellular verification signalsbetween the wide area cellular network and a cellular terminal via thewire telephone network connector. Thus, wireless telephone calls whichare routed to the cellular terminal via the base station, when thecellular terminal is within the local region covered by the basestation, may be secured by exchange of data between the cellular networkand cellular terminal over the wire telephone network via the wiretelephone connector and the base station. Calls from the public switchedtelephone network including the wide area cellular network which arerouted through the base station can thus employ the same securitysystems and methods which are employed by the wide area cellularnetwork.

In a preferred embodiment, the telephone base station includes a couplerwhich is adapted for cooperatively mating with a cellular terminal whichis parked in the base station. The coupler couples the cellular securityinformation between the cellular terminal and the base station. Cellularsecurity information can include encryption keys that are relayed fromthe wide area cellular network to the cellular terminal via the wiretelephone connector for use in encrypting communications with the basestation.

Enhanced security is provided by relaying the security informationbetween the cellular terminal and the base station when the cellularterminal is parked in the base station, to avoid their radio frequencytransmission. Exchanged security information can also includeauthentication signals that bilaterally verify both the identity of thecellular phone to the cellular network and the identity of the networkto the phone, as described in U.S. patent application Ser. No.08/043,758 and U.S. Pat. No. 5,091,942, the disclosure of both of whichare hereby incorporated herein by reference.

As an alternative to physically mating the terminal with the basehowever, signals may be relayed between the cellular terminal and thecellular network, via the base station and the wire network connector,by using radio frequency transmission over cellular frequencies, betweenthe cellular terminal and the base station. This radio frequencytransmission may be necessary when verification and encryption signalsare exchanged upon reactivation of the base station, when the cellularterminal moves outside the local region and then returns to the localregion. Telephone communication between the terminal and the publicswitched network via the base station is prevented unless the relayedcellular verification signals indicate that the radio telephonecommunication is authorized.

The base station and the cellular terminal may also exchange localverification information, separate from the cellular verificationinformation, for communications between the base station and terminalwhen the terminal is within the local region and is receivingcommunications via the wire telephone network connector from the wiretelephone network. Thus, the wide area cellular network need not becontacted in order to provide security for local communications betweenthe cellular terminal and the base station within local region for callsoriginating from the wire telephone network.

It will be understood by those having skill in the art that the localauthentication procedure preferably uses the same protocol as thecellular telephone verification procedure. The local authentication keyis preferably exchanged when the cellular terminal is parked in the basestation, via the coupler, but may also be established by exchangingradio frequency transmissions. Local encryption keys may also beestablished along with local authentication keys. Telephonecommunication between the terminal and the wire telephone network viathe wire telephone network connector on a subsequent occasion isprevented unless the exchanged local authentication signals areconsistent with the previously established authentication information.

The above described security systems serve two primary purposes. Firstthey prevent an unauthorized cellular terminal from making calls via abase station for which someone else will be billed. Second, they preventeavesdropping, which is otherwise easy when communications aretransferred from the hardwired medium to the radio medium.

Eavesdropping may be prevented by the use of digital voice transmissionusing digital encryption. Digital encryption typically requires the useof a secret quantity or "key" known only to the cellular terminal andthe base station with which it is communicating. One function of thesecurity system is thus to establish this common key.

It is more secure to establish the key for encryption of conversationsseparately for each call, instead of using the same key forever,although the exposure risk in using the same key for several calls issmall. Such temporary keys can be formed by combining a secret key witha random number upon call set up.

The secret key or A-key is preferably stored in both the cellularterminal and the base station or network in a non-accessible manner. Atcall set up, the base station transmits a random number RAND to thecellular terminal. The cellular terminal combines RAND and A-key toobtain a temporary key "B-key" and the base station does the same. TheB-key is then used for encrypting further communication between the twounits until it is overwritten by a subsequent exchange. If the transferof the number to be called is part of the encrypted furthercommunications, an unauthorized cellular terminal, that is unable togenerate the correct B-key because it does not have access to the A-key,will not be able to continue and set up a call, thus preventing usefulunauthorized access.

The above description shows that appropriate encryption may alsoinherently prevent fraud. An alternative technique of denyingunauthorized access may also be used, called "authentication". Inauthentication, a random number RAND is transmitted from the basestation to the cellular terminal as described above. The RAND is in thiscase known as an authentication challenge. The cellular terminalcombines RAND with A-key to obtain a response RESP to the challenge, andtransmits RESP to the base station. The base station also locallycomputes RESP and checks the received version against its locallycomputed version. If they do not match, access is denied.

Authentication alone however does not guarantee that access will bedenied to a fraudulent cellular terminal. For example, one couldconstruct a false base station that issues many random challenges to agenuine cellular terminal in its vicinity and records the correspondingresponses, increasing the probability of having in its memory achallenge-response pair that the real base station will accept. Evenworse, it can initiate a call to the real base station, wait for thereal base station to issue a challenge, then temporarily shut off itstransmitter just as the genuine cellular terminal replies with RESP.When the real base station indicates it has accepted the call, thefraudulent base station starts up its transmitter again at a sufficientpower level to overpower the genuine cellular terminal, and can thenproceed to set up a call.

Encryption can be used to prevent these fraudulent practices, and can beused in combination with the authentication techniques described above.Encryption security depends on preventing access to the long-term secretA-key. This can be done by providing a device, such as an integratedcircuit chip, that includes the A-key embedded in electronic form, anauthentication algorithm processor, an electrical input for RAND and anelectrical output for RESP and/or B-key.

The chip preferably provides no access to read out the A-key, andperforms only one operation, namely to respond to a challenge with RANDby returning RESP and B-key. The internal processor buss that must beable to access the internally stored A-key is not accessible external tothe chip and can even be prevented from access under a microscope andmicroprobe system by covering the chip with a metallic screening layer.Such a device is employed in the European GSM cellular system and isknown as a "smart card". In one form it is supplied to subscribers bytheir service providers in a thin, plug-in card like a credit-card.

The A-key of every subscriber for such a security system is stored in asecure computer somewhere in the cellular system. Information on aparticular subscriber is stored in the network in his Home LocationRegister (HLR) which is part of a cellular exchange belonging to theservice provider with whom he has a subscription. When a subscriber useshis cellular terminal to access a visited network (VLR), the cellularterminal first transmits its telephone number to the VLR. The VLR canidentify that subscriber's HLR from the telephone number and contactsthe HLR via a telephone trunk signalling system known as signallingsystem no. 7 in Europe, or via a system called IS41 in the U.S. The VLRthen requests security variables from the HLR that can be used to verifythe mobile's claimed identity and/or to encrypt the conversation, thatis a RAND/RESP pair and a B-key. To reduce use of the trunk lines,several RAND/RESP/B-key triplets can be sent by the HLR to the VLR inthe same transaction, sufficient perhaps for a day's use at the visitedlocation.

Another threat to the security of such a system is the possibility ofunauthorized access to signalling system no. 7 or IS41 lines, whichconnect all telephone exchanges together, even those in differentcountries and continents. An unauthorized request to an HLR for securityvariables pertaining to particular telephone number can then be made. Ifthe VLR were permitted to specify RAND, a previously used RAND could bespecified and then the fraudulent VLR would receive a B-key that had therecorded call to be deciphered. Therefore, the VLR should not be allowedto specify the RAND, but rather it should be generated extemporaneouslyby the HLR. However, the fraudulent VLR would still receive a validsecurity triplet. This may not be useful for making fraudulent calls, asthe real VLR would again contact the HLR and would receive new tripletsnot possessed by the fraudulent VLR. Nevertheless, it is preferable toprevent a fraudulent VLR from receiving any security informationpertaining to any subscriber. This can be prevented if the HLR firstissues only the RAND to the VLR, the VLR transmits it to the cellularterminal, the cellular terminal replies with RESP and the VLR conveysRESP to the HLR. Only if the HLR confirms the identity of the cellularterminal would it then release a B-key and possibly further triplets.

The above described technique may still allow a false VLR to extractRAND/RESP pairs from genuine cellular terminals in the hope ofcollecting sufficient pairs to provide a high probability of being ableto make a fraudulent access to the real system. This is prevented byintroducing the bilateral authentication procedure described in theaforementioned patent application and U.S. patent that were aboveincorporated by reference. In a preferred implementation of bilateralauthentication, the cellular terminal first identifies itself to theVLR. The VLR determines the cellular terminal's HLR from the ID andcontacts the HLR for security variables. The HLR extemporaneously issuesa random challenge RAND and computes the B-key and two responses, RESP1and RESP2 by combining RAND with the identified subscriber's A-key. TheHLR releases the RAND and the first response RESP1 only to the VLR. TheVLR transmits RAND and RESP1 to the cellular terminal. The cellularterminal combines RAND with its stored A-key and also generates RESP1,RESP2 and B-key, and compares the generated RESP1 with the receivedRESP1. If they match, then it can confirm that the VLR has been incontact with the genuine HLR. It then sends RESP2 to the authenticatedVLR. The VLR sends RESP2 to the HLR and the HLR compares its generatedRESP2 with the received RESP2. If they match, this confirms to the HLRthat the VLR is in contact with the genuine cellular terminal. The HLRthen releases the B-key to the VLR for encrypted communication with thecellular terminal, and possible further sets of RAND, RESP1, RESP2 andB-key, now called security quadruplets.

Thus, a preferred embodiment of the present invention implements theabove described security features in the base station. It is desirablethat the station not contain the highly secret A-key known only to thecellular terminal and its HLR. However, this may be allowed if the keyis supplied in secure "smart card" form to the base station as well asto the cellular terminal. However, an alternative is described below.

If the station is not to contain permanent security information, itmust, like the VLR, obtain such information from the HLR. Since the basestation is connected to the PSTN via the normal wireline telephoneinterface, it can ring up the HLR, for example using a special 800service number, and request security quadruplets. Since that servicenumber can be rung by any PSTN subscriber, it is even more important toprotect against fraudulent requests for security information than forthe more obscure "fraudulent VLR" threat. Therefore the HLR releasesfirst only the extemporaneously generated RAND, waits for the basestation to convey it to the cellular terminal and receive the replyRESP, and then will only release a B-key to the microbase if the correctRESP is relayed to it. The base and the cellular terminal respectivelythen use the B-key to encipher communications between them for apredetermined time or amount of calls thereafter. The base station can,like the HLR, receive a bundle of quadruplets that can be used for aperiod such as a day or for a defined number of calls before contactwith the HLR is again required for new security variables.Alternatively, user option can trigger the base station to seek newvariables, with use of the previous set being cycled randomly from callto call until the user decides to renew the set. In this way, the secretA-key is never required to be stored in the base station nor aresecurity quadruplets stored that could be useful in obtainingunauthorized cellular access or in deciphering cellular calls.

Moreover, the base station can be arranged to erase all storedquadruplets upon both loss of power and loss of the telephoneconnection. Exchange of security information with the wide area cellularnetwork via the public switched telephone network and exchange ofsecurity information between the base station and cellular terminal,would then be initialized or reinitialized upon detection of connectionor reconnection of the wire telephone network connector to the wiretelephone network and/or to the power supply outlet. Thus, new securityvariables are reestablished after the base station has been moved. Therelaying of verification and encryption signals, by the base station tothe wide area cellular network via the wire telephone network,preferably takes place each time the cellular terminal returns fromoutside the local region back to the local region, but the frequencywith which this is done is optional. This operation, referred to as"reactivation", ensures that the proper cellular terminal is operatingwith the base station.

Preferably, the cellular verification signals include a temporary keywhich is provided by the cellular network and which is stored in thebase station as part of the verification exchange between the cellularnetwork and the cellular terminal via the base station. This temporarykey is preferably used for all communications between the cellularterminal and the base station while the cellular terminal is within thelocal region, whether or not these communications originate from thewide area cellular network (via the wire telephone network), or from thewire telephone network.

Once the cellular terminal moves outside the local region, the temporarykey may be erased from the base station so that a new temporary key mustbe obtained from the wide area cellular network via the wire telephonenetwork upon reentry into the local region. Alternatively, this can be auser option as discussed above. The use of a temporary key can allowmultiple calls to take place within the local region using a singletemporary key. Long term security is not affected, however, because anew temporary key can be obtained at any time. Moreover, long termsecurity is not impacted because the permanent key of the cellulartelephone is not stored in the base station. Secure radio personalcommunication system and methods are thereby provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically illustrate a radio personal communicationssystem including a base station and a cellular terminal, with radiocommunications between the terminal and the base station, andalternatively radio communications between the terminal and a wide areacellular network, respectively.

FIG. 2 illustrates a front perspective view of an embodiment of a basestation of the present invention, with a terminal shown in hidden lines.

FIG. 3 is a schematic block diagram of a base station according to thepresent invention.

FIG. 4 is a schematic block diagram of a base station transceiveraccording to the present invention.

FIG. 5 is a schematic block diagram of a radio personal communicationscellular terminal according to the present invention.

FIG. 6 is a flowchart illustrating operations during initialization of aradio personal communications system according to the present invention.

FIG. 7 is a schematic illustration of a first cell re-use pattern for awide area cellular network.

FIG. 8 is a schematic illustration of a second cell re-use pattern for awide area cellular network illustrating a method of allocating basestation frequency according to the present invention.

FIG. 9 is a flowchart illustrating operations of a radio personalcommunications system according to the present invention.

FIGS. 10A and 10B together form a flowchart illustrating securityoperations in a radio personal communications system according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art.

Referring now to FIGS. 1A and 1B, conceptual diagrams of a radiopersonal communications system according to the present invention areshown. Such a system operates within a cellular communications networkwhich allocates portions of a plurality of frequencies (channels) withina spectrum to separate geographic cells. Thus, the system provides awide area wireless communications network having the capacity to providehigh quality wireless communications to a large number of users with alimited number of frequencies allocated to the wide area cellularnetwork. As shown in FIG. 1A, a wide area cellular network includes atleast one radio network cell station 102, such as a cellular telephonecell station, for transmitting and receiving messages in a network cellrange indicated by 104, via cell antenna 106. The range 104 of radionetwork cell station 102 is typically represented graphically asillustrated in FIGS. 1A, 1B, 7 and 8. Radio network cell station 102also interfaces with the wire network 108 in special trunk andsignalling lines. It will be understood by those having skill in the artthat a wide area cellular network 100 typically includes many radionetwork cell stations 102 to cover a large area as illustrated in FIGS.7 and 8. In such a system each radio network cell station 102 covers acell (range) 104 within wide area cellular network 100 and may beconnected to a Mobile Switching Center (MSC), which is a special form oftelephone exchange for mobile phones, via special landlines or microwave(wireless) links. The MSC is in turn connected to the PSTN 108 viaspecial trunk and signalling lines to provide connectivity between anyradio network cell station 102 of cellular network 100 and the outsideworld.

Still referring to FIG. 1A, a telephone base station 110 is locatedwithin the cell (range) 104 of a network cell station 102 of wide areacellular network 100. Base station 110 includes a low power transceiverfor transmitting and receiving via base station antenna 112, over alimited base station range 114, typically on the order of tens ofmeters. Thus, a base station may be used for transmission and receipt ofradio personal communications in a home or office. Base station 110 alsois electrically connected to the wire network 108, for example by anormal telephone jack socket. Wire network 108, is also referred to asthe Public Switched Telephone Network (PSTN). PSTN 108 is the regular"wire line" telephone system supplied by, for example, the regional BellOperating Companies, and may use copper wire, wireless local loopextensions, wideband cable, optical fiber, or other stationarytransmission channels. Base station 110 may be wired directly to PSTN108 (in a domestic application for example) or connect through a PABX(not shown) in an office environment, for example.

Still referring to FIG. 1A, a radio personal communications terminal 120is shown for radio communications with either base station 110 or radionetwork cell station 102 via antenna 122. Radio personal communicationsterminal 120, also referred to herein as a "cellular terminal" or simplya "terminal", includes a radio telephone such as a cellular phone.Terminal 120 may also include, for example, a full computer keyboard anddisplay, a document scanner, and full graphics and multimediacapabilities.

As illustrated in FIG. 1A, when terminal 120 is in the range 114 of thebase station 110, a radio link 124 therebetween is established. As shownin FIG. 1B, when the terminal 120 is outside the range 114 of the basestation 110, but within the range (cell) 104 of the network cell station102, a new radio link 126 is automatically established with the networkcell station 102 to establish communications through wide area cellularnetwork 100. Thus, when the user is relatively close to the base station110 (i.e. within the home or office), wireless communications take placewith the base station so that the wide area cellular network, with itshigher billing rate structure, is bypassed. When the user is relativelyfar from the base station 110, communications take place with thecellular network.

It will be understood by those having skill in the art that a completeradio personal communications system will typically include many basestations 110, terminals 120 and radio network cell stations 102. It willalso be understood by those having skill in the art that conventionalcommunications and handoff protocols may be used with the presentinvention, and need not be described further herein. For purposes ofthis description, it will be assumed that the spectrum allocation forthe radio network cells is the IS-54B cellular phone spectrum allocationwhich is illustrated in Table 1 below.

                  TABLE 1                                                         ______________________________________                                                              Boundary Transmitter Center                             Bandwidth   Number of Channel  Frequency (MHz)                                System (MHz)    Channels  Number MOBILE BASE                                  ______________________________________                                        Not Used         1               (824.010)                                                                            (869.010)                             A.sup.•                                                                         1        33       991    824.040                                                                              869.040                                                         1023   825.000                                                                              870.000                               A      10       333        1     825.030                                                                              870.030                                                         333    834.990                                                                              879.990                               B      10       333       334    835.020                                                                              880.020                                                         666    844.980                                                                              889.980                               A'     1.5       50       667    845.010                                                                              890.010                                                         716    846.480                                                                              891.480                               B'     1.5       83       717    846.510                                                                              891.510                                                         799    848.970                                                                              893.970                               ______________________________________                                        Transmitter                                                                           Channel Number Center Frequency (MHz)                                 ______________________________________                                        MOBILE   1 ≦ N ≦ 799                                                                   0.030 N + 825.000                                              990 ≦ N ≦ 1023                                                                 0.030 (N - 1023) + 825.000                             BASE     1 ≦ N ≦ 799                                                                   0.030 N + 870.000                                              990 ≦ N ≦ 1023                                                                 0.030 (N - 1023) + 870.000                             ______________________________________                                    

In the radio personal communications system described in FIGS. 1A and1B, it is important to avoid same channel interference between basestation 110 and the radio network cell station 102. Same channelinterference can be avoided by using two discrete spectra for thenetwork calls and for the base station. For example, the base stationcan use cordless telephone protocols and frequencies. Unfortunately,this requires the terminal 120 to operate under both cellular andcordless protocols, which may be costly and wasteful.

According to the invention, the operator of network 100, which hastypically been assigned the use of a specific plurality of frequencieswithin a frequency spectrum of a designated geographic region by aregulatory authority, is allowed to assign frequencies and optionallypower levels, of base station 110. The wide area cellular networkoperator (provider) can assign frequencies and optionally power levelsto base station 110 to minimize same channel interference and tomaximize revenue from the assigned frequency spectrum.

According to the invention, base station 110 uses the obtained frequencyand power level, respectively, to govern operation of base station 110.Frequency and power level signals may be obtained at the same time asthe aforementioned security information, and may also be used to controloperation of the radio personal communications (cellular) terminal 120as will be described below. As will also be described below cellularterminal 120 may be controlled to operate at the same frequency andpower level as base station 110. Alternatively, a different frequencyand power level may be provided. Thus, the wide area cellular networkoperator has the opportunity to receive revenue from the provision offrequencies and security variables, while simultaneously preventingradio communications between base station 110 and terminal 120 frominterfering with communications within cellular network 100. Even if thecellular operator declines this revenue in the interest of competition,the enhanced security provided by the present invention environment canhelp to attract new customers to the cellular operator's network.

An embodiment of a base station and cellular terminal according to thepresent invention is illustrated in FIG. 2. Base station 110 includeshousing 130 which is adapted to cooperatively mate with cellularterminal 120 and provide an electrical interface between base station110 and cellular terminal 120 using electrical connector 132 or otherelectrical connector means. Base station 110 is connected to a powersource (power outlet) by power line connector 134 or other powerconnection means and to a wire telephone network by a wire telephonenetwork connector 136 extending from base station 110 to within housing130 or other means for electrically connecting base station 110 to awire telephone network. As shown in FIG. 2, housing 130 is preferablyportable to allow the user to move it and reinstall it in differentlocations. Base station 110 as illustrated in FIG. 2 may further includebattery charger connector 138 or other charger interface means whichconnects battery powered cellular terminal 120 to a battery charger (notshown in FIG. 2) when cellular terminal 120 is inserted or parked inhousing 130 as illustrated by hidden lines in FIG. 2. Sensor 140 detectswhen cellular terminal 120 is parked in housing 130 and the batterycharger is activated to charge the battery of battery powered cellularterminal 120. It will be understood by those having skill in the artthat a separate sensor 140 need not be used to detect when terminal 120is parked in housing 130.

Base station 110 as illustrated in FIG. 2 can also include display 142or other user indicating means. Alternatively, cellular terminal 120 mayinclude an indicating means which may be used to display signals frombase station 110 transmitted over electrical connector 132 when cellularterminal 120 is parked in housing 130. Base station 110 may also includekeyboard 144 or other user input means. Alternatively, as with display142, cellular terminal 120 may include an input means which may be usedto provide inputs to base station 110 when cellular terminal 120 isparked in housing 130. Optionally, the base station 110 can include aninterface 135 with the normal domestic wire line phone which would ringin response to incoming calls only if the cellular terminal was switchedoff or is otherwise unreachable.

A block diagram of an embodiment of a base station 110 of the presentinvention is illustrated in FIG. 3. Power supply 150 is connected topower line connector 134 and provides the power supply voltages to thecircuitry of base station 110. Power supply 150 further includes powerdetection means 151 for detecting when the connection of power lineconnector 134 to the power source has been lost and for providing asense signal to control processor 154 indicating that power has beenlost.

Ringing current and exchange battery voltage detector 152 iselectrically connected to wire telephone connector 136 and includesmeans for detecting an incoming call on wire telephone connector 136which is connected to wire telephone network 108. Detector 152 furtherdetects if the electrical connection of wire telephone network 108 toconnector 136 has been lost. Detector 152 supplies signals to controlprocessor 154 when an incoming call "ring" is detected and when theconnection to wire telephone network 108 is lost. An indication that thewire telephone network (line) connection has been lost may then be sentto display 142 under the control of control processor 154. Controlprocessor 154 can also control switch 98 to connect an incoming call tothe normal wire line phone interface or jack 135 when the cellular isunreachable. Alternatively, this connection may serve a fax machine.

Control processor 154, in cooperation with ringing current and exchangebattery voltage detector 152 provides activation means for initiatingcommunications between wire telephone network 108 and cellular terminal120 through base station 110 when cellular terminal 120 is within region114. For incoming calls from wire telephone network (line) 108, detector152 detects the incoming call and sends an activation signal to controlprocessor 154 which in turn controls subsequent communicationsoperations of base station 110. For calls initiated from cellularterminal 120, control processor 154 detects the communication fromcellular terminal 120 received by transceiver circuit 164 or other radiotransceiving means connected to antenna 112 at a selected frequencywithin the spectrum of wide area cellular network 100. Control processor154 sends a control signal to detector circuit 152 to generate OFF-HOOKand other signals such as pulse dialling that may be necessary tointerface with a loop-disconnect line interface such as is typicallyused by wire telephone network 108. A smart card interface 97 may alsobe provided.

Splitter circuit 156 effects a split of the two-wire, bidirectionaltelephone audio signal into a four-wire system of separate send andreceive signals. Received signals from the wire telephone network 108are converted from analog to digital by analog to digital converter (Ato D) 158 while transmit signals to wire telephone network 108 areconverted from digital to analog by digital to analog converter (D to A)160. This allows all of the subsequent audio signal processing to becarried out digitally using digital signal processors. Echo canceler 162attenuates echoes of the signal sent through connector 136 to PSTN wirenetwork 108 to inhibit corrupting of the signal received from the PSTN.Echo canceler circuit 162 further prevents echoes being transmitted tocellular terminal 120 by transceiver circuit 164 or other radiotransceiving means connected to antenna 112.

On incoming calls over wire telephone network (line) connector 136,transceiver circuit 164 responds to the ring detect from detector 152under the control of processor 154 to communicate with cellular terminal120 using a selected frequency within the frequency spectrum of the widearea cellular network 100. Storage circuit 155 or other storage means iselectrically connected to control processor 154 to provide a storagecapacity for program and data information such as a frequency indicatingsignal representing the selected frequency. Storage circuit 155 mayinclude conventional readable and writable memory such as RAM or EEPROM.

After echo cancellation, modem 166 processes received digitized audiosignals to extract any digital control messages that might be receivedalong with the audio signal from the wire telephone network (line). Suchdigital control messages may for example be programming information forbase station 110 transmitted by the operator of wide area cellularnetwork 100. Extracted digital control messages are passed to controlprocessor 154. Modem 166 may perform data/speech discrimination. Adigital signal processor such as Texas Instruments type TMS320C56 may beused for echo canceler 162 and modem 166.

Received digitized speech is passed to transceiver 164 for transmission.The digitized speech may first be compressed by compression circuit, notshown, to a lower bit rate using a conventional speech decodingalgorithm such as CELP or VSELP. In an analog transmission embodiment ofbase station 110 of the present invention a conversion circuit, notshown, reconverts the discriminated speech to an analog signal formodulating transceiver 164 which in this embodiment is an analogtransceiver.

Radio signals from cellular terminal 120 to base station 110 received byantenna 112 are detected and converted to digital speech signals bytransceiver 164. The digital speech signals are then passed to echocanceler circuit 162 and modem circuit 166 for transmission on wiretelephone network (line) connector 136 to wire network 108.Alternatively, the received signals may be digitized to complex numberform, using for example the LOGPOLAR technique described in U.S. Pat.No. 5,048,049. The complex number stream is then passed to modem 166 fornumerical demodulation and conversion to analog speech for sending onthe wire telephone line.

The present invention may also be used for data transmission fromcellular terminal 120 when cellular terminal 120 either incorporates apersonal computer system or by plugging cellular terminal 120 into apersonal computer to connect the computer to modem circuit 166 withoutthe use of a direct wire telephone line cable connection to thecomputer. When handling data transmissions, modem circuit 166 andtransceiver 164 translate the data stream between the over-the-airprotocols used and normal wire telephone line data transmissionprotocols. Transceiver 164 may also detect when the received signal hasreverted to voice and, responsive to control processor 154, effect areversion of modem circuit 166 and echo canceler circuit 162 to theprocessing of voice signals.

Transceiver 164 may be selected to generate and receive signalsconforming to any standard, for example, AMPS, ETACS, NMT450, NMT900,GSM, DCS1800 or IS54. In addition, transceiver 164 may generate orreceive signals conforming to air-interface standard for communicationswith satellite systems, such as INMARSAT-M, INMARSAT-P, IRIDIUM,ODYSSEY, GLOBALSTAR, ELLIPSAT or M-SAT. All such standards may beutilized with the present invention to provide communications fromcellular terminal 120 through normal PSTN wire lines 108 and avoidingusing the wide area system.

FIG. 4 illustrates a schematic block diagram of a radio transceiver 164of FIG. 3. As shown, transceiver 164 includes circuitry for both thereception and transmission of the radio frequency signals. Signalsreceived by the antenna 112 are directed to the receive circuits by theduplexer 201. The duplexer is a filter with two separate bandpassresponses: one for passing signals in the receive band and another forpassing signals in the transmit band. Duplexer 201 allows simultaneoustransmission and reception of signals by using different receive andtransmit frequencies. For example, in the IS54 architecture, the receiveand transmit frequencies are separated by 45 MHz.

After passing through the duplexer 201, received signals are amplifiedby a low noise radio frequency (RF) amplifier 202. This amplifierprovides enough gain to overcome the loss of duplexor 201 and filter203, and to swamp noise of mixer 204. After amplification, unwantedcomponents of the signal are filtered out by the receive filter 203.After filtering, the signal is mixed down to a first intermediatefrequency (IF) by mixing it in mixer 204 with a second signal generatedby the channel synthesizer 215 and filtered by Local Oscillator (LO)filter 214. The first IF signal is then amplified by amplifier 205 andunwanted mixing products are removed by IF filter 206. After filtering,the first IF is mixed in mixer 207 to yet another lower frequency orsecond IF signal, using a signal provided by local oscillatorsynthesizer 216. The second IF signal is then filtered by two filters208 and 210, and amplified by multistage amplifiers 209 and 211 toobtain an IF signal 212 and a radio signal strength indication (RSSI)signal 213. Thereafter, it undergoes a process of digitization, forexample, as described in U.S. Pat. No. 5,048,059 to Dent, the disclosureof which is incorporated herein by reference.

In order to transmit, a datastream 219 is generated by modem 166 (FIG.3). In IS54 architecture, the datastream is organized as bursts for timedivision multiplexing with other users. Reference oscillator 218generates a precise frequency which is used as a stable reference forthe RF circuits. The output of oscillator 218 is passed through amultiplier 221 where it experiences a sixfold increase in frequency.This frequency is then passed into a quadrature network 222 whichproduces two signals of equal amplitude which have a quadrature phaserelationship, i.e. they are offset by 90°. These quadrature signals,along with the datastream 219, are combined in the modulator 223 tocreate a modulated signal, as described in an article entitled I and QModulators for Cellular Communications Systems, D. E. Norton et al.,Microwave Journal, Vol. 34, No. 10, October 1991, pp. 63-79. Themodulated signal is passed to a mixer 224 which translates the signal toradio frequency. The exact radio frequency is determined by the localoscillator signal provided by the channel synthesizer 215. The radiofrequency signal is passed through a variable gain controlled amplifier225. The gain of this amplifier, which is controlled by means of avoltage on transmit power control line 220, determines the eventualoutput power, since the linear power amplifier 227 has fixed gain.Filtering is performed by transmit filter 226.

Referring now to FIG. 5, the design of terminal 120 is similar to thatof base station 110 (FIG. 3) except that a ringing current and exchangebattery voltage detector 152 are not present. As illustrated in FIG. 5,cellular terminal 120 includes transceiver 250 or other means forcommunicating with wide area cellular network 100 when cellular terminal120 is not within the base region (range) 114 of base station 110 andfor communicating with transceiver 164 of base station 110 when cellularterminal 120 is within base region 114. Transceiver 250 is connected toantenna 122. Cellular terminal 120 further includes its own controlprocessor 254 and storage means 255 similar to those described withrespect to base station 110 and transmit circuit 251 and receive circuit253 for receive and transmit signal processing respectively.

As further shown in FIG. 5, when terminal 120 is a cellular phone, itincludes a keypad 257, a display 259, a speaker 261, and a microphone263. In order to provide a computer communications terminal for receiptand transmission of audio, video and data and/or multimedia signals,keypad 257 may be a full scale personal computer keyboard and display259 may be a large graphics display. A document scanner 265 may also beprovided as may other devices 267 such as disk drives and modems. Thedesign of terminal 120 is well known to those having skill in the artand need not be described further herein.

As described above, radio communications between base station 110 andcellular terminal 120 occurs at a frequency assigned by the wide areacellular network provider to avoid same channel interference betweenbase station 110 and network cell station 102. In the embodiment of thepresent invention described above, the channel selection means whichobtains the channel within the cellular spectrum of wide area cellularnetwork 100 for communications between cellular terminal 120 and basestation 110 is included in base station 110. For non-multiplexedsystems, any given frequency is one channel; however, for multiplexedtype systems each frequency may carry multiple communications channels.The present invention will be further described referring to frequency,however, it is to be understood that in a multiplexed system basestation 110 may be assigned a specific channel or slot using suchselected frequency.

The selected frequency may be entered into base station 110 fromexternal to base station 110 as an extracted digital control message, asdescribed above, in which case the frequency indicating signal isreceived by base station 110 by wire line communications over connector136. The frequency indicating signal is converted to a synthesizercommand and applied to line 217 to produce the requisite transmit andreceive frequency. The power level indicating signal is converted to atransmit power control signal and applied to line 220 to control thetransmit power. The conversions are preferably performed by controlprocessor 154 using conventional techniques. Operations performed to setthe frequency, and optionally power level, will be described below inconnection with FIG. 6.

The frequency indicating signal from the operator of wide area network100 is selected to minimize interference between base station 110 andnetwork cell station 102. Preferably, a frequency is utilized which isone of the frequencies within the cellular spectrum which is notallocated to the network cell station 102 in the cell 104 in which basestation 110 is located. More preferably, a frequency is selected fromthe group of frequencies within the cellular spectrum which is allocatedto a cell of wide area cellular network 100 which is farthest from saidbase station as illustrated in FIGS. 7 and 8.

The circuitry of base station 110 as illustrated in FIG. 3 furtherfunctions as a requesting means within housing 130, electricallyconnected to wire telephone line connector 136, for communicating withthe operator of wide area network 100 over wire network 108 using apredetermined service number stored in storage circuit 155. Controlprocessor 154 initiates a call using the predetermined service number bysending control and a data signals representing a request. Modem 166 andconverter 160 are used to transmit the request over line 136 as a knowntype of carrier which may be detected by a modem (not shown) set up forthis purpose by the operator of wide area cellular network 100. Theoperator of wide area cellular network assigns a frequency manually orautomatically, to reduce or avoid frequency interference. The requestedfrequency indicating signal from the operator of wide area cellularnetwork 100 is then received by modem 166 and an extracted digitalcontrol message is provided to control processor 154 as described above.An indication of the selected frequency is stored in storage circuit155, based upon the received frequency indicating signal. Alternatively,frequencies can be assigned via a removable frequency indicator, such asa "smart card" as described in copending application Ser. No. 08/093,076to Rydbeck entitled Method and Apparatus for Controlling TransceiverOperations in a Radio Communication System, assigned to the assignee ofthe present application, the disclosure of which is hereby incorporatedherein by reference.

A frequency indicating signal is also provided to cellular terminal 120when terminal 120 is parked in base station 110 and stored in storagemeans 255 as an indication of the selected frequency so that bothcellular terminal 120 and base station 110 have the selected frequencyinformation. Alternatively, the frequency information may be provided tocellular terminal 120 using the wide area cellular network 100 ifcellular terminal 120 is not parked in base station 110 and the userdoes not wish to park the terminal before initiating communicationsbetween base station 110 and cellular terminal 120 following a change inthe selected frequency.

The process of requesting a frequency indicating signal may be initiatedby the operator as an input using keyboard 144, for example, by pressing#0 to initiate calling the predetermined service number. Alternatively,the request may be initiated by control processor 154 responsive to alost connection signal from detector 152. The lost connection signal mayindicate that the connection of wire telephone line 136 to wiretelephone network 108 has been lost or that both the telephoneconnection and the power connection, based on the signal from powerdetection means 151 to control processor 154 have been lost, asdescribed above. Thus, the detector 152, power detection means 151 andcontrol processor 154 determine when a new frequency selection isrequired and initiate such a request.

Alternatively, the selected frequency information may be entered intobase station 110 using keyboard 144 which would likewise pass theinformation to control processor 154. This allows the user of basestation 110 to separately obtain the selected frequency information fromthe operator of wide area cellular network 100 and then manually inputthe data through keyboard 144.

The means for requesting and receiving the frequency indicating signalmay also be contained in cellular terminal 120. If this is the case,cellular terminal 120 may contact the operator of wide area cellularnetwork either through network cell station 102 or using telephone lineconnector 136 while cellular terminal 120 is parked in base station 110.Likewise, the input means for manually entering the request for afrequency indicating signal may be keypad 257 of cellular terminal 120.

If base station 110 is moved to a new location, any selected frequencypreviously used may be invalid and likely to cause interference withwide area cellular network 100 if transmissions from base station 110are allowed to occur without obtaining a new selected frequency from theoperator of wide area cellular network 100. It is desirable that basestation 110 include means responsive a detected loss of telephoneconnection or telephone and power connection loss as described above forpreventing transmission by transceiver 164 using the previously selectedfrequency. This may be readily accomplished by the circuitry illustratedin FIG. 3, as control processor 154 receives indicating signals fromboth detector circuit 152 and power detection means 151 which togetheract as a means for detecting loss of telephone and/or power connection.Control processor 154 may then control transceiver 164 to preventfurther transmissions. Control processor 154 may further send anindication to display 142 indicating that a new frequency needs to beobtained. Control processor 154 may also send a message to the operatorof the wide area cellular network via the PSTN network.

Initialization and channel acquisition operations of an embodiment ofthe personal communications system of the present invention areillustrated in the flow chart of FIG. 6. Operations are initialized atblock 300 when base station 110 is obtained by the user and plugged intoa normal domestic telephone jack with telephone connector 136 and poweroutlet with power connector 134. On power up, detector 152 notifiescontrol processor 154 that a telephone connection has been establishedto wire telephone line 108 and power sense signal from power detectionmeans 151 notifies control processor 154 that line power has beenconnected. At block 302 base station 110 calls the wide area cellularnetwork using a predetermined service number. The service number can bestored in base station 110, requiring only one or two keypad depressionson keyboard 144 to effect dialling or may be initiated automatically asdescribed above. Alternatively, as described above, the user may contactthe wide area cellular provider using a different phone and PSTN lineand verbally request set-up information which may then be manually keyedinto base station 110. The service number can appropriately be an "800"type number that is valid from all locations. According to theinvention, set up information is only issued after the aforementionedauthentication procedure is successfully completed, thus denyingfraudulent use of frequency channels.

After the call is initiated at block 302, base station 110 notifies thewide area cellular network operator of the location of base station 110at block 304. Using signalling facilities available in modern digitaltelephone networks, this may be accomplished by having the wide areacellular network operator request from the PSTN the number of the phoneline originating the call. At block 306 base station 110 requests acontrol message including a frequency, from the wide area cellularnetwork operator. The request may also include power level and channelinformation as well as frequency. At block 308 base station 110 receivesa control message including an indication of the requested frequencyfrom the wide area cellular network operator. This is then stored as anindication of the received frequency in base station 110 at block 310.

Base station 110 then transmits an indication of the received frequencyto cellular terminal 120 at block 312. This transmission may beaccomplished when cellular terminal 120 is parked in base station 110using system connector 132. Alternatively, a frequency indicating signalmay be transmitted by radio communications using transceiver 164 ifcellular terminal 120 is not parked in base station 110. Such atransmission may be made using the last frequency assigned to basestation 110 by the cellular network operator. Optionally, when it isnecessary to reallocate the base frequency when cellular phone 120 isnot parked in base station 110, the wide area network operator may placea call to cellular phone 120 over the cellular network and send a datamessage informing cellular terminal 120 of the change to the basefrequency. However, if the base frequency will not be frequentlyreallocated, base station 110 may notify the user of the need to parkcellular terminal 120 to obtain the new frequency information bydisplaying a warning message on display 142. At block 314 cellularterminal 120 stores an indication of the received frequency in cellularterminal 120.

Once the operating frequency for communications between base station 110and cellular terminal 120 has initially been established, the assignedfrequency will continue to be valid so long as base station 110 remainsin the same location. However, should base station 110 be moved to a newlocation, interference with the wide area cellular network could resultas the previously assigned frequency for base station 110 may be used inthe local cell of the wide area cellular network where base station 110is reinstalled. Consequently, at block 316 base station 110 determinesif the telephone connection to the base station has been lost since theindication of the requested frequency was last received as describedabove. Base station 110 may further determine if the power connection tobase station 110 has been lost since the indication of the requestedfrequency was last received. If the telephone connection or,alternatively, the telephone and power connections have been lost sincethe indication of the requested frequency was last received, basestation 110 repeats steps 300 through 314 as described above.Alternatively, at step 316 when it has been determined that theconnections have been lost base station 110 communications may bedisabled until a new request for a selected frequency is initiated.

The above operations were described for an embodiment using the basestation processor and keyboard to acquire the frequency information. Inan alternative embodiment the keyboard and processor of cellularterminal 120 may be used to carry out the initialization operations. Inthis embodiment, all of the steps of FIG. 6 would be carried out whilecellular terminal 120 was parked in base station 110. The communicationswith the wide area cellular network operator could then be handled bycellular terminal 120 with base station 110 serving to transmit signalsbetween cellular terminal 120 and the network operator over PSTN 108.

It is preferred that base stations 110 not be allocated frequencies thatare already in use in the cell of the wide area cellular network inwhich base station 110 is located, but to choose frequencies in use inthe cell which is a maximum distance away. Allocation of frequency bythe wide area cellular network provider in one embodiment is illustratedin FIG. 7. FIG. 7 illustrates a 21-cell frequency reuse pattern which isemployed in some United States wide area cellular networks to avoidinterference between neighboring cells. It is to be understood that awide area cellular network 100 may include a plurality of such reusepatterns, and thus include greater than the 21 cells illustrated in FIG.7. Each cell 104 in a cluster of 21 uses a different 1/21 fraction ofthe total number of frequencies available to the wide area cellularprovider. FIG. 7 shows the distribution of 21 groups of frequenciesnumbered 1 to 21 in a regularly spaced cell lattice. It may be seen thatthe cells using the same frequency groups are equispaced and root(21)cell diameters between centers where cell diameter is defined as thediameter of the inscribed circle of each hexagon.

It may be seen in FIG. 7 that cells numbered 15 or 8 are those mostdistant from the cells numbered 1. Therefore, the frequencies thatshould be used for base stations 110 located within cells numbered 1should be drawn from frequency groups 8 and 15. Reciprocally, thefrequencies used for base stations 110 located in cells numbered 15should be drawn from frequency groups 1 and 8 and so on for cellsnumbered 8. By symmetry, base stations 110 in cells numbered 2 shoulduse frequencies drawn from groups 9 and 16 and so forth. Thus, basestations 110 within each region may employ 2/21 of the total number offrequencies available. If this contains at least 21 frequencies, then a21-cell re-use plan can be employed to ensure that cells using the samefrequency are at least root(21) cell diameters apart. This requires thatthe total number of frequencies employed in both the cell and cellsystems is at least 21×21/2=220. This condition is normally satisfied inthe U.S. AMPS system, where two competing operators share over 800channels, having more than 400 each. Thus it is desirable that the cellsshould be capable of being programmed and reprogrammed to optimumfrequencies from the mobile telephone network according to the cell inwhich they are located.

FIG. 8 illustrates how base frequency allocations may be made in thecase of a cell re-use pattern such as the tighter, 7-cell pattern suchas may be employed in the European GSM system. As shown in FIG. 8,within each cell, different areas are allocated different sets offrequencies for use by base stations 110 located within thosesubregions. In FIG. 8, the frequency allocation patterns for basestations 110 are illustrated for the cells numbered 1 and 5respectively.

FIG. 9 illustrates a method for operation of the radio personalcommunications system once the frequency information has been acquiredby base station 110 and its associated cellular terminal 120. Operationsbegin when power is applied to cellular terminal 120 at Block 352. Uponapplication of power, cellular terminal 120 scans the selected frequencyallocated to its associated base station 110 at Block 354, anddetermines if a signal level above threshold has been detected, at Block356. If a signal level above threshold has been detected, then terminal120 is within the range 114 of its associated base station 110. Cellularterminal 120 then communicates at Block 360 over PSTN 108 by wirelesscommunications to base station 110. If a signal level above thresholdwas not detected, then the terminal 120 is not within the range 114 ofbase station 110 and communications are initiated with network cellstation 102 at Block 358, using conventional techniques.

It will be understood by those having skill in the art that a separatevoice channel frequency and power level may be used for transmissions bybase station 110 and terminal 120. The power levels may be different forthe base station and the terminal if, for example, the base station hasa larger antenna or a more sensitive receiver. It is also contemplatedthat the frequencies will be different since the terminal and basestation would not typically transmit or receive on the same frequenciesin a duplex transceiver. The base station and cellular terminal mayalternatively employ time duplex on a single frequency, such as the 902mHz "unlicensed band". Alternatively, a single frequency and power levelmay be obtained from the wide area cellular provider and a secondfrequency and power level may be determined from the single frequencyand power level.

Accordingly, the network provider/operator may allocate frequencies andpower levels of base station-to-terminal communications. By allocatingthe frequency and power level of base station-to-terminalcommunications, same frequency interference within a network cell isreduced and the network provider obtains additional revenue from thelicensed frequency spectrum for the base station.

Referring now to FIGS. 10A and 10B, security operations in a radiopersonal communications system according to the present invention willnow be described. It will be understood by those having skill in the artthat these operations are preferably performed by stored programinstructions in control processor 154 of FIG. 3. However, they may alsobe performed by stored program instructions in other components of FIG.3, and may also be performed by special purpose hardware such asapplication specific integrated circuits (ASIC).

Referring to FIG. 10A at Block 402, connection or reconnection of thebase station 110 to the wire telephone network (PSTN) 108 via wiretelephone network connector 136 is detected by detector 152 of FIG. 3 totrigger security operations. A test is made at Block 404 as to whetherthe cellular terminal 120 is parked in base station 110. Similarexchanging operations 410 and relaying operations 420 are thenperformed, except that these operations are performed via transceiver164 (FIG. 3) if the terminal is not coupled to base station 110 and areperformed via connector 132 if the terminal is coupled to the basestation. Preferably the operations are performed when parked so thatradio frequency transmission of security information is avoided.However, when the cellular terminal reenters the local region of thebase station, these operations may need to be performed via radio.Operations performed via transceiver 164 will be designated by thesuffix "a" in FIG. 10A, while operations performed via connector 132will be designated by the suffix "b" in FIG. 10A.

Still referring to FIG. 10A, an exchange of verification information forlocal communication with the wire network is performed at Blocks 412aand 412b. As used herein, "local communication" refers to communicationbetween the base station and cellular terminal, within the local region,for wire network calls or cellular network calls. It will be understoodby those having skill in the art that base station 110 and cellularterminal 120 may include verification and encryption protocols whichgovern local communications for wire network calls. In particular, theverification and encryption protocols are preferably the cellularnetwork verification and encryption protocols so that duplication ofprotocols are not required. However, separate identification numbers andencryption keys may be used to govern local communications with the wirenetwork. As shown in Blocks 414a and 414b, local communication with thewire network is prevented unless the exchange of verificationinformation authenticates the cellular terminal. Accordingly, theoperations of Blocks 412a, 412b and 414a, 414b, allow exchange of localtelephone verification information with the cellular terminal forcommunications with the wire network when the cellular terminal iswithin the local region.

Still referring to FIG. 10A, operations 420 for relaying verificationand encryption information between the wide area cellular network andthe cellular terminal, via the base station and the wire network, willnow be described. As shown in Blocks 422a, 422b, terminal identificationfor cellular communications is accepted. As known to those having skillin the art, a cellular phone typically includes an identification numberwhich is unalterably stored in the cellular telephone. A similararrangement is provided in cellular terminal 120. Cellular telephoneprotocol is used to communicate this identification to the base station.As shown in Blocks 424a, 424b, the terminal identification is relayed tothe cellular network via the wire network. At Blocks 426a, 426b,verification and encryption information for cellular communication isreceived from the cellular network via the wire network after thepreferred security exchanges discussed above. At Blocks 428a, 428b,cellular verification and encryption information is exchanged betweenthe terminal and base station, under the direction of the wide areacellular area network via the wire network, using transceiver 164 orpreferably via connector 132. As shown at Block 430, cellularcommunications from the cellular network via the wire network areprevented unless verification authenticates the cellular terminal.

Authenticating a cellular terminal's claimed ID by the security methodsand systems of the present invention allows the base station to be usedby visiting subscribers. The normal cellular network is specificallyadapted to handle such "roamers", but the wireline network or PSTN doesnot allow visitors to make calls from another subscriber's phone withautomatic transfer of the billing to the caller's phone. According tothe invention, this feature is provided within the PSTN. A method andsystem which permit service of visiting cellular terminal to anon-native base station will now be described.

The visiting cellular terminal first identifies itself to the basestation upon attempting to initiate a call. They then perform twooperations, the order of which can be varied with greater or lessersecurity implications and operational impacts. The details are a matterof design choice.

Operation 1: The base station identifies the visiting cellularterminal's cellular service provider's service (800) number from astored table and contacts it via the PSTN to obtain security variables.After the previously discussed security exchanges, the base stationobtains a B-key from the service provider, but not necessarily in thiscase a frequency. The frequency used was already provided by the basestation's registered service provider and remains so.

Operation 2: The base station switches to communicating with thevisiting cellular terminal in encrypted mode to receive the desirednumber to be called, and then invokes an automatic billing transfermechanism to place the call via the PSTN. The PSTN receives the visitingcellular terminal's telephone number and the desired number to becalled. The onus is on the PSTN to verify the visiting cellularterminal's ID and accept or deny the call. The PSTN may for example denythe call simply if there is no commercial agreement for automaticbilling transfer between the visited phone system and the visitor'sservice provider.

Referring now to FIG. 10B, assuming that the wide area cellular networkhas authenticated the cellular terminal, multiple local calls may beaccepted and made via the wire network, or from the cellular network viathe wire network, using the local verification information as shown atBlock 436. If cellular encryption is used (Block 432), then cellularencryption is also used for the local communication.

Still referring to FIG. 10B, as shown at Block 438, multiple local callscontinue as long as the terminal is within the local region. Once theterminal is outside the local region, then at Block 440, the terminaloperates using the cellular verification information and encryption likea standard cellular telephone. The base station is not involved in thesecommunications and may be deactivated until the terminal is again withinthe cordless range as shown at Block 452. For example, when the cellularnetwork detects that the cellular terminal has been registered as activein another locality, a deactivating message may be sent to the basestation. Reactivation operations 450 then take place. As part ofdeactivation, the temporary key in the base station is erased, at Block442 so that upon reactivation, a new temporary key will be requiredbefore allowing communications with the cellular terminal via the basestation. Optionally, the keys can be rotated for the next call.

In order to generate a cellular type radio signal which iscomprehensible to a cellular terminal having a unique secret key whichis electronically stored therein and is not possible to extract, thebase station must be capable of encrypting and decrypting the encipheredmessages. In order to avoid the base station from having to beprogrammed with or to receive the secret key from the wire telephonenetwork, which can be a security hazard, the secret key is preferablytransformed at call setup into a temporary key that is used only forthat call or for a short time. If the temporary key is for any reasoncompromised, it only effects the security of that call and not the longterm security of the secret key. Thus, the key received by the basestation is preferably a temporary key rather than the permanent keywhich is stored in the cellular terminal.

Upon reactivation, a test is made at Block 456 as to whether theterminal is coupled to the base station, and relaying operations 420begin again. The base station will automatically dial the mobile phoneservice node for appropriate reprogramming and then relay the dialdigits to the wide area cellular network for effecting routing of thecall. The wide area cellular network can then appropriately issue theauthentication challenge to verify the terminal's identity and establisha new temporary encryption key in both the terminal and the basestation. When the base station is activated due to the cellular systemhaving accepted registration of the cellular terminal in the local area,then any reauthentication performed over the cellular network resultingin a new temporary key should preferably be copied to the base stationso that calls received on the home number and converted to cellularsignals can be correctly encrypted and decrypted. It will be understoodby those having skill in the art that the exchanging operations 410 mayalso be performed again although preferably they are not performed againuntil the wire network connection is lost, indicating that the basestation has been moved.

Accordingly, the present invention allows the base station which isconnected to the wire telephone network, to handle the calleridentification and verification methodology which is employed by thecellular system to prevent telephone fraud. The cellular systemcommunicates to the base station over the wide area network, for exampleusing a predefined cellular network service number. The cellularterminal is thereby linked to the wide area cellular network, via thebase station and wire network, preferably while the cellular terminal isphysically parked in the base station. The terminal key or a temporaryterminal key is thereby made available. The base station preferablyconverts the handshake from the cellular terminal to wire telephonenetwork line signals rather than direct radio transmissions from theterminal to the wide area cellular network. These operations can beperformed on system activation or reactivation at the same time asfrequency allocation occurs.

As described, the base station and terminal can also have their ownencryption key for use in linking between the two for localcommunications with the wire telephone network. Thus, antifraudprotection may be provided when the terminal is acting simply as a localphone linked by the base station to the wire network, without requiringinterface with the wide area cellular provider.

As also described, the base station also can handle the encryptionmethodology that is used by the cellular system. Preferably, a newtemporary key is not obtained by the base station for each call. Rather,the temporary key is assigned on system activation and is used for allsubsequent communications between the base station and the terminaluntil reactivation is required. Optionally, the base station andterminal can have their own key for use in linking between the two,which is assigned and shared between the base station and the terminalwhen the terminal is physically plugged into the base station.

It is also to be understood that the present invention may be usedwithin any cellular type wireless communications structure where acellular type structure is understood to encompass any systemincorporating any type of channel reuse pattern over a wide areacommunications network.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

That which is claimed:
 1. A telephone base station for connecting a wiretelephone network to a cellular terminal within a local region of a widearea cellular network, said telephone base station comprising:wiretelephone network connecting means, for connecting said base station tosaid wire telephone network; means for relaying cellular verificationsignals between said wide area cellular network and a cellular terminal,via said wire telephone network connecting means; and detecting means,electrically connected to said wire telephone network connecting means,for detecting if the electrical connection between said wire telephonenetwork and said wire telephone network connecting means has beenlost;wherein said relaying means is responsive to said detecting meansfor preventing radiotelephone communication between said cellularterminal and said base station via said wire telephone networkconnecting means, after loss of the electrical connection to said wiretelephone network, unless said relaying means again relays cellularverification signals between said wide area cellular network and saidcellular terminal, via said wire telephone network connecting means. 2.The telephone base station of claim 1 further comprising:coupling means,electrically connected to said relaying means, and adapted tocooperatively mate with a cellular terminal so that an electricalconnection is provided between the cellular terminal and the basestation when the cellular terminal is parked in the telephone basestation, for coupling said cellular verification signals between saidcellular terminal and said relaying means through the electricalconnection when the cellular terminal is parked in the telephone basestation.
 3. The telephone base station of claim 2 wherein said relayingmeans further relays cellular encryption signals between said wide areacellular network and said cellular terminal, via said wire telephonenetwork connecting means.
 4. The telephone base station of claim 1further comprising:radio transceiving means, electrically connected tosaid relaying means, for coupling said cellular verification signalsbetween said cellular terminal and said relaying means.
 5. The telephonebase station of claim 4 wherein said relaying means further relayscellular encryption signals between said wide area cellular network andsaid cellular terminal, via said radio transceiving means.
 6. Thetelephone base station of claim 1 further comprising:means forexchanging local telephone verification signals with said cellularterminal, for communications therewith when said cellular terminal iswithin said local region.
 7. The telephone base station of claim 6further comprising:coupling means, electrically connected to saidexchanging means, and adapted to cooperatively mate with a cellularterminal so that an electrical connection is provided between thecellular terminal and the base station when the cellular terminal isparked in the telephone base station, for coupling said local telephoneverification signals for verifying the cellular terminal between saidcellular terminal and said exchanging means through the electricalconnection when the cellular terminal is parked in the telephone basestation.
 8. The telephone base station of claim 6 furthercomprising:radio transceiving means, electrically connected to saidexchanging means, for coupling said local telephone verification signalsbetween said cellular terminal and said exchanging means.
 9. Thetelephone base station of claim 6 wherein said exchanging means furthercomprises means for preventing radiotelephone communication between saidcellular terminal and said wire telephone network via said wiretelephone network connecting means unless the exchanged localverification signals indicate that said radiotelephone communication isauthorized.
 10. The telephone base station of claim 9 wherein saidpreventing means comprises means for decrypting the called number. 11.The telephone base station of claim 1 further comprising means forreceiving cellular encryption keys from said cellular network via saidwire telephone network connecting means.
 12. The telephone base stationof claim 8 further comprising means for exchanging encryption signalswith said cellular terminal, via said radio transceiving means.
 13. Thetelephone base station of claim 1 wherein said cellular verificationsignals include a temporary key which is stored in said base station.14. The telephone base station of claim 13 wherein said relaying meansfurther comprises means for preventing radiotelephone communicationbetween said cellular terminal and said wide area cellular network viasaid wire telephone network connecting means unless the relayed cellularverification signals indicate that said radiotelephone communication isauthorized.
 15. The telephone base station of claim 14 wherein saidpreventing means comprises means for decrypting the called number. 16.The telephone base station of claim 13 further comprising:power lineconnecting means; and battery charging means electrically connected tosaid power line connecting means, for charging a battery in a cellularterminal which is cooperatively mated thereto.
 17. The telephone basestation of claim 13 further comprising means for detecting that saidcellular terminal is outside said local region, and for erasing apreviously used temporary key from said base station in responsethereto.
 18. The telephone base station of claim 13 further comprisingmeans for detecting that the cellular terminal is outside said localregion and for rotating the use of said temporary keys in responsethereto.
 19. A security method for a telephone base station whichconnects a wire telephone network to a cellular terminal within a localregion of a wide area cellular network, said security method comprisingthe following steps which are performed by the telephone basestation:detecting if the electrical connection between the wiretelephone network and the base station has been lost; and relayingcellular verification signals between the wide area cellular network anda cellular terminal, via the wire telephone network wherein saidrelaying step is preceded by said detecting step and wherein saidrelaying step further comprises the step of preventing radiotelephonecommunication between the cellular terminal and the base station afterloss of the electrical connection to said wire telephone network untilagain relaying cellular verification signals between the wide areacellular network and the cellular terminal, via the wire telephonenetwork.
 20. The security method of claim 19 wherein said relaying stepcomprises the step of relaying the cellular verification signals forverifying the cellular terminal between the wide area cellular networkand the cellular terminal through an electrical connection providedbetween the cellular terminal and the base station when the cellularterminal is parked in the base station.
 21. The security method of claim20 wherein said relaying step further comprises the step of relayingcellular encryption signals between the wide area cellular network andthe cellular terminal, when the cellular terminal is parked in the basestation.
 22. The security method of claim 19 wherein said relaying stepcomprises the step of relaying cellular verification signals between thewide area cellular network and the cellular terminal via radiotransmission, when the cellular terminal is within the local region. 23.The security method of claim 22 wherein said relaying step furthercomprises the step of relaying encryption signals between the wide areacellular network and the cellular terminal, via radio, when the cellularterminal is within the local region.
 24. The security method of claim 19further comprising the following step which is performed by thetelephone base station step:exchanging local telephone verificationsignals with the cellular terminal, for communications therewith whensaid cellular terminal is within said local region.
 25. The securitymethod of claim 24 wherein said exchanging step comprises the step ofexchanging the local telephone verification signals for verifying thecellular terminal between the wide area cellular network and thecellular terminal through an electrical connection provided between thecellular terminal and the base station when the cellular terminal isparked in the base station.
 26. The security method of claim 25 whereinsaid exchanging step further comprises the step of exchanging cellularencryption signals with the cellular terminal, when the cellularterminal is parked in the base station.
 27. The security method of claim24 wherein said exchanging step comprises the step of exchanging thelocal telephone verification signals between the wide area cellularnetwork and the cellular terminal via radio transmission, when thecellular terminal is within the local region.
 28. The security method ofclaim 27 wherein said exchanging step further comprises the step ofexchanging cellular encryption signals with the cellular terminal, viaradio, when the cellular terminal is within the local region.
 29. Thesecurity method of claim 24 further comprising the following step whichis performed by the telephone base station:preventing radiotelephonecommunication between said cellular terminal and said wire telephonenetwork via the base station, unless the exchanged local verificationsignals indicate that said radiotelephone communication is authorized.30. The security method of claim 29 wherein the cellular verificationsignals include a temporary key which is stored in said base station.31. The security method of claim 27 further comprising the followingstep which is performed by the telephone base station:preventingradiotelephone communication between said cellular terminal and saidwire telephone network via the base station, unless the relayed cellularverification signals indicate that said radiotelephone communication isauthorized.
 32. The security method of claim 31 wherein said preventingstep comprises the step of encrypting and decrypting the called number.33. The security method of claim 30 further comprising the followingsteps which are performed by the base station:detecting that thecellular terminal is outside said local region; and erasing saidtemporary key in response thereto.
 34. The security method of claim 30wherein said relaying step is preceded by the following step which isperformed by the base station:detecting reentry of the cellular terminalinto the local region.
 35. The telephone base station of claim 1 furthercomprising means for receiving a frequency indicating signal from saidwide area cellular network.
 36. The telephone base station of claim 35wherein said frequency indicating signal receiving means comprises meansfor receiving said frequency indicating signal only if said cellularverification signals are accepted by said cellular network.
 37. Atelephone base station for connecting a wire telephone network to acellular terminal within a local region of a wide area cellular network,said telephone base station comprising:wire telephone network connectingmeans, for connecting said base station to said wire telephone network;means for relaying cellular verification signals between said wide areacellular network and a cellular terminal, via said wire telephonenetwork connecting means; means for exchanging local telephoneverification signals with said cellular terminal, for communicationstherewith when said cellular terminal is within said local region; anddetecting means, electrically connected to said wire telephone networkconnecting means, for detecting if the electrical connection betweensaid wire telephone network and said wire telephone network connectingmeans has been lost;wherein said exchanging means is responsive to saiddetecting means for preventing radiotelephone communication between saidcellular terminal and said base station, after loss of the electricalconnection to said wire telephone network, unless said exchanging meansagain exchanges local verification signals with said cellular terminal.38. A security method for a telephone base station which connects a wiretelephone network to a cellular terminal within a local region of a widearea cellular network, said security method comprising the followingsteps which are performed by the telephone base station:relayingcellular verification signals between the wide area cellular network anda cellular terminal, via the wire telephone network; detecting if theelectrical connection between the wire telephone network and the basestation has been lost; and exchanging local telephone verificationsignals with the cellular terminal, for communications therewith whensaid cellular terminal is within said local region wherein saidexchanging step is preceded by said detecting step wherein saidexchanging step further comprises the step of preventing radiotelephonecommunication between the cellular terminal and the base station, afterloss of the electrical connection to said wire telephone network, untilagain exchanging local verification signals with the cellular terminal.39. The security method of claim 29 wherein said preventing stepcomprises the step of encrypting and decrypting the called number. 40.The telephone base station of claim 35 further comprising reactivationdetecting means, for detecting reentry of said cellular terminal intosaid local region, said relaying means being further responsive to saidreactivation detecting means.
 41. The telephone base station of claim 35further comprising telephone connecting means, for connecting said basestation to a wire telephone.